You are correct that ``wm_uncertainty_ns`` is basically the same as ``decl_err``, and, since it's defined in the database, you can use it to sort columns in a way that you can't use ``ra_err``.

But... this looks really inconsistent to me. Both the naming -- if we call the error on RA ``ra_err``, we should call the error on decl ``decl_err`` -- and the formatting -- why can I sort the decl error column but not the RA one? Obviously, there's a technical reason why not, but it's sad if that technical reason intrudes into the UI. I think either both columns should be sortable or neither, but not one of them.